4G SIM Card

Comviq Offer

So today I got an SMS from Comviq inviting me to get a 4G SIM for free (the reality is if you order through their phone service you are charged 95SEK, but if you order online it's free).Because I had some difficulties with their website, I called (that's when I found out about the 95SEK charge).The conversation seemed to me to be more about getting me to open a contract account and/or eliciting my personal details - personnummer, address etc - than about the SIM. So, my questions are these - Why can't the 3G data on my current SIM, sitting quietly in its iPhone 6, be updated over the air? Is there really such a thing as a 4G SIM?Is such a card really a necessity? Thanks in advance for any technologically sound advice!